In water flow testing, it is important that the flow entering and leaving the test section or model be as noise-free as possible. Due to the high speed of sound in water (approximately 5,000 feet per second), the flow noise can cause pressure fluctuations in the test section which unfavorably disturb test readings occurring therein. This noise may be caused by turbulence, flow separations, flow angularity, or a combination of these factors anywhere in the piping system. Thus, it is desirable that the test facility create a minimum of flow noise that will interfere with noise created by the test model.
One such instance where noise in the test facility is of concern is in testing the complex internal flow fields of the hot gas manifold of a rocket engine, such as the Space Shuttle main engine. During operation, this manifold operates under extreme conditions and requires a certain amount of back pressure to function at peak efficiency. During testing, water flow through this manifold can have velocities as high as 150 feet per second and at a flow rate of 5,000 gallons per minute. In the past, one of the methods for providing the required back pressure involved using a flexible rubber collar making an orifice centered therein and a constrictive band around the exterior of the collar. The collar was positioned in the flow downstream the manifold being tested, and when it was desired to impart selected back pressure to the manifold, the band was tightened, reducing the diameter of the orifice the flow passed through. One of the problems with this collar, however, was that the rubber it was composed of was flexible enough to be drawn into the vacuum downstream of the venturi effect caused by the orifice which overly constricted flow and created an abnormal flow pattern through the collar, in turn causing noise which would propagate upstream to the test model. This situation, in some instances, was so extreme that excessive back pressure resulted in possible model damage.
To overcome these problems, applicants have provided a valve that smoothly accelerates flow therethrough and discharges the high velocity jet into a dump tank, virtually eliminating flow noise which may propagate upstream and disturb readings taken from the test model. Further, this valve is adjustable from near closed to fully open flow positions, enabling it to provide a selectable back pressure and flow rate to the hot gas manifold or model being tested.
It is, therefore, an object of the present invention to provide a low noise valve that smoothly accelerates fluid flowing therethrough and further provides selected back pressure and flow rate upstream from the valve.